Fig. 3(a) shows the effect of pH on the membrane fouling. The
highest S/N ratio was determined at pH 10 and S/N ratio decreased
with decreasing pH value. Hence, membrane was fouled more
severe at pH 4.In literature, it was reported that the isoelectric point
of FMNP010 membrane is 4.2 . The occurrence of an isoelectric
point means that a lower pH than the isoelectric point, the membrane is positively charged and vice versa . So, surface charge of
FMNP010 is negative at high pH values and negative charge density
increases as the pH increases. Also, many of the dissolved components in the pulp and paper wastewater are negatively charged
[25]. Lower membrane fouling was obtained at pH10 due to
the increasing electrostatic repulsion forces between negatively
charged membrane surface and negatively charged components
in wastewater that preventing the adsorption of solutes on to the
membrane.